Almost done getting used to the N2 printer. Just did my first dual extrusion. Worked nice. My plan is to have my students make some 3D Prints with conducting PLA and test the resistance within the model.

If I replace the yellow in the following image with black conducting filament I want the filament to have full infill, however I think you can only set infill for both extruders. Any suggestions how to set infill at 100% for only one extruder and the default 10% for the other?

dualinfil.png (9.46 KiB) Viewed 5517 times

The above print looks fine, but the below print shows only 10% infill with the yellow, which when the yellow is replaced with conducting filament will not conduct as well than if it is solid. Any suggestions? I guess the solution is to make both extruders 100% infill.

Not familiar with conducting filament, but if you want to increase the infill of one nozzle, you need to increase the other one together.The currently ideaMaker doesn't take this setting apart for two nozzles.

Normally when fill density over 60%-70%, it is almost like a solid part.

As Vicky has pointed out, IM applies the same infill percentage to both extruders. The easy fix is to set the infill to 100%, but another trick might be to play with the number of shells. I just printed a part with 5 shells and the effect was that the small section areas were effectively printed solid, whilst most of the thicker sections were filled at the infill percentage. This may work for your model.

Why are you using a raft? With the time and filament you are putting into the raft, you could print the item at 100% directly on the bed and save both.

Please let us know how you get on with your conductive filament experiments. From what I have read, the resistivity is quite high, even on the so-called 'low resistivity' filaments,

tja wrote:I just printed a part with 5 shells and the effect was that the small section areas were effectively printed solid, whilst most of the thicker sections were filled at the infill percentage. This may work for your model.

Thanks tja, that is a brillant suggestion, I will try that when the ProtoPasta conductive filament comes in.

Most of the conductive inks etc that I have tested so far have not been very good. I will post what I fined out. The chance to have my students make little LED embedded devices is too cool to pass up. P.S. Most LED's need some resistance, just not too much

The reason I use the raft is that my builds seem to attach better, I am also a bit scared of wrecking my BuildTac with a hard to remove print. I guess I could always crank the bed temperature up if I can't remove the print. Any other suggestions.

walshlg wrote:Another idea is to design the fill yourself as part of your model.

I use Blender which is fairly difficult since it is mainly for animation not 3D Printing and is difficult to make objects manifold for 3D Printing. Are you suggesting I make the object have it's own layers or inside columns? See image.

I think that would work especially if I combine it with the other shell suggestion.

My conductive protopasta filament arrived today. Here are some images and my Ideamaker settings file using the left extruder for the conducting filament and the right extruder for the regular (insulating) PLA and raft.

Given current progress in the technology of conductive filament I think that is not too bad a result. Perhaps to better demonstrate the concept to your students you could increase the voltage to make the LED appear brighter. Some of the later type LEDs are quite bright when forward biased with around 10mA. Using a small 12V battery for example might be better for demonstration purposes.

With the resistance values you have measured and the appropriate supporting electronics, this filament opens up many possibilties for practical use, resistive touch sensors for one.

walshlg wrote:I strongly suggest that you give annealing a try, it might improve conductivity a lot

I like the idea of after printing covering the object and raising the printbed to about 80 C, then reducing the print bed temperature over a few hours to room temperature. The other idea is to anneal in the oven but once it is removed from the printbed expect warping.

Curious if the resistivity will reduce. Any other suggested temperatures and durations for annealing?

So I tried annealing for only a few hours. Build plate at 110 C, glass cup upside down over the print. Got the PLA to about 60 C and the Conducting to about 75 C. Then let it cool over half hour to about 45 C and tested the resistance. Seemed to reduce all resistance by about 600 ohm.

I did not feel like this was anywhere near long enough, but reasonably impressed with the reduction in resistance. Contacted Protopasta to see if they have any temperature suggestions. I will do a bit more testing with an oven on the weekend.

OK here is an idea, perhaps if you annealed with current going through it would reinforce the conductive pathway!! Try inserting something like a spade plug and anneal with maybe 100mA and see if that improves conductance! Might be a waste of time but might not!

walshlg wrote:OK here is an idea, perhaps if you annealed with current going through it would reinforce the conductive pathway!! Try inserting something like a spade plug and anneal with maybe 100mA and see if that improves conductance! Might be a waste of time but might not!

Someone better with electricity than me might want to look at this. Could we just use electricity to heat the conducting filament and then really slowly let it cool? Not quite sure of voltages or currents that would work, but I try to keep my Robotics class assignments below both 12V and 2 Amps for safety reasons. I am fairly sure 120 V is a really bad idea.

Sounds like a Physics 12 problem:

How many joules of electrical energy will raise the temperature of 3 grams of Conductive PLA from 25 C to 100 C given that the Thermal Conductivity for normal PLA = 0.13 W / m K. Assuming the resistance is 2000 Ohms and you must use a voltage that is reasonably safe.

I think I am just going to see how hot I can get a 2K resistor.

...

That was interesting at about 17 V DC it just kind of went brown, but the outside did not register much change with my IR thermometer.